It consumes less power than X1900XTX crossfire.
Some other things were that the 7950GX2 takes up 2 slots like the 7900GTX. For quad SLi, its just like putting together 7900GTX SLi.
INQ also mentioned its quite. (Im interested at this because the fan is rather small and probably as a high rpm).
The cool thing is, you buy a 7950GX2 (OCed 7900GT SLi setup) and a 7600GS or something. The 7950GX2 goes to the first PCI-e slot, while the 7600GS goes to the second PCI-e slot. While you enjoy SLi performance, you can use the 7600GS as your "PPU" for HavokFX physics.
Prices are $550~ USD according to some shops. SOme guy in hardocp bought a XFX 7950GX2 XXX version already.
It looks like availbility and price may not be the problem as its already in stock around the world.